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United States Patent |
6,169,138
|
Petit
,   et al.
|
January 2, 2001
|
Foamed pressure sensitive tapes
Abstract
The present invention relates to a pressure sensitive adhesive foam with a
percentage of theoretical density less than 90, wherein the foam has a
peel adhesion of greater than about 1 N/cm and a compression set under
constant deflection of less than about 60%. The present invention further
includes a pressure sensitive adhesive foam comprising a thermoplastic
block copolymer, a tackifying resin; an isocyanate terminated monomer or
oligomer; a polymer comprising a backbone selected from the group
consisting of polybutadiene, polyester and polyether, wherein the polymer
contains at least 2 active hydrogens capable of reacting with the
isocyanate terminated monomer; and expandable particulate materials. The
present invention further includes a pressure sensitive adhesive foam
comprising a thermoplastic olefin polymer or copolymer, having a density
less than 0.91 g/cm.sup.3 and a torsion modulus less than 18 MPa, and a
tackifying resin; and, optionally, plasticizing oil and expandable
particulate materials, or glass microspheres. The invention finally
further comprises a method of forming the above film.
Inventors:
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Petit; Dominique (Housse, BE);
Ladang; Michel (Herve, BE)
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Assignee:
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Saint-Gobain Performance Plastics Corporation (Wayne, NJ)
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Appl. No.:
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091133 |
Filed:
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June 4, 1998 |
PCT Filed:
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June 10, 1996
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PCT NO:
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PCT/US96/10107
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371 Date:
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June 4, 1998
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102(e) Date:
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June 4, 1998
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PCT PUB.NO.:
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WO97/47681 |
PCT PUB. Date:
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December 18, 1997 |
Current U.S. Class: |
524/500; 428/40.1; 428/40.2; 428/40.3; 428/42.1; 428/325; 428/327; 428/338; 428/339; 428/343; 428/352; 428/354; 428/406; 428/407; 428/441; 428/500; 521/139; 521/140; 524/502; 524/505 |
Intern'l Class: |
C08J 057/02; C08L 077/00; B32B 033/00; 42.1 |
Field of Search: |
428/40.1,40.2,308,325,327,338,339,343,352,354,355,406,441,500,407,40.4,41.3
521/139,140
524/500,502,505
|
References Cited
U.S. Patent Documents
3615972 | Oct., 1971 | Morehouse, Jr. et al. | 156/79.
|
4223067 | Sep., 1980 | Levens | 428/308.
|
4430479 | Feb., 1984 | Merton et al. | 525/127.
|
4483889 | Nov., 1984 | Andersson | 427/389.
|
4731066 | Mar., 1988 | Korpman | 604/366.
|
4855169 | Aug., 1989 | McGlothlin et al. | 428/35.
|
4855170 | Aug., 1989 | Darvell et al. | 428/40.
|
5024880 | Jun., 1991 | Veasley et al. | 428/317.
|
5180635 | Jan., 1993 | Plamthottam et al. | 428/345.
|
5244996 | Sep., 1993 | Kawasaki et al. | 526/347.
|
5272208 | Dec., 1993 | Shiraki et al. | 525/92.
|
5342858 | Aug., 1994 | Litcholt et al. | 521/98.
|
5455111 | Oct., 1995 | Velasquez Urey | 428/315.
|
5475075 | Dec., 1995 | Brant et al. | 526/348.
|
5681654 | Oct., 1997 | Mamish et al. | 428/354.
|
5780523 | Jul., 1998 | Petit et al. | 521/137.
|
5869555 | Feb., 1999 | Simmons et al. | 524/229.
|
Foreign Patent Documents |
84220 | Jul., 1983 | EP | .
|
349216 | Jan., 1990 | EP | .
|
2237945 | Jul., 1974 | FR | .
|
2250513 | Jun., 1992 | GB | .
|
57-137375 | Aug., 1982 | JP | .
|
59-155479 | Sep., 1984 | JP | .
|
63-202680 | Aug., 1988 | JP | .
|
1313581 | Dec., 1989 | JP | .
|
7070520 | Mar., 1995 | JP | .
|
94/13459 | Jun., 1994 | WO | .
|
95/25774 | Sep., 1995 | WO | .
|
Other References
120: 325387W Peelable pressure-sensitive adhesives, Chemical Abstracts vol.
120, 1994, p. 86.
|
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Porter; Mary E.
Parent Case Text
This application is a continuation-in-part of U.S. Ser. No. 08/877,060,
filed Jun. 17, 1997, now U.S. Pat. No. 5,780,523, which is a continuation
of now abandoned U.S. Ser. No. 08/356,100, filed Dec. 15, 1994.
Claims
What is claimed is:
1. A pressure sensitive adhesive foam, wherein the foam has a peel adhesion
of greater than about 1 N/cm, comprising:
a) at least one olefinic polymer, having a density less than 0.91
g/cm.sup.3 and a torsion modulus less than 19 MPa;
b) at least one tackifying resin; and
c) at least one particulate material, selected from the group consisting of
expandable particulate material comprising a polymeric shell and a
volatilizable fluid core; and glass spheres.
2. The pressure sensitive adhesive foam of claim 1, comprising from about
99.5 to about 65% by weight of a pressure sensitive adhesive polymer
composition having a peel adhesion greater than about 10 N/cm and from
about 0.5 to about 35% by weight of an expandable particulate material
comprising a polymeric shell and a volatilizable fluid core.
3. A pressure sensitive adhesive foam according to claim 1, having a
density of less than about 70% of the theoretical density, wherein the
foam has a peel adhesion of greater than about 20 N/cm and a compression
set of less than about 60% and wherein the foam comprises:
a) from about 5 to about 80% by weight of at least one olefinic polymer
having a density less than 0.91 g/cm3 and a torsion modulus of less than
18 MPa;
b) from about 15 to about 80% by weight of at least one tackifying resin;
c) from about 0.5 to about 30% by weight of at least one plasticizing oil;
and
d) from about 2 to about 25% by weight of expandable particulate materials
comprising a polymeric shell and a volatilizable liquid core.
4. A pressure sensitive adhesive foam according to claim 1 in which the
olefinic polymer is selected from the group consisting of polyethylene,
polypropylene, polybutene and poly-methylpentene, and copolymers thereof,
and mixtures thereof.
5. A pressure sensitive adhesive foam according to claim 1 in which the
tackifying resin is selected from the group consisting of rosins and rosin
derivatives, hydrocarbon resins and terpene resins.
6. A pressure sensitive adhesive foam according to claim 5 in which the
tackifying resin is a hydrocarbon resin selected from the group consisting
of glycerine rosin ester, hydrogenated pentaerythritol ester, hydrogenated
glycerine ester, modified tall oil rosin, polymerized rosin and rosin
ester.
7. A pressure sensitive adhesive foam according to claim 4 in which the
olefinic polymer is selected from the group consisting of polyethylene,
copolymers of ethylene and mixtures thereof.
8. A pressure sensitive adhesive foam according to claim 7 in which the
copolymers are polymerized using monomers selected from the group
consisting of butene, hexene, octene and methylpentane.
9. A pressure sensitive adhesive foam according to claim 7 in which the
monomers are alpha-olefins.
10. A pressure sensitive adhesive foam according to claim 1, having a
density of less than about 40% of the theoretical density, wherein the
foam has a peel adhesion of greater than about 20 N/cm and a compression
set of less than about 20% and wherein the foam comprises:
a) from about 10 to about 50% by weight of at least one olefinic polymer
having a density less than 0.91 g/cm3 and a torsion modulus of less than
18 MPa;
b) from about 25 to about 70% by weight of at least one tackifying resin;
c) from about 2 to about 20% by weight of at least one plasticizing oil;
and
d) from about 2 to about 25% by weight of expandable particulate materials
comprising a polymeric shell and a volatilizable liquid core.
11. A pressure sensitive adhesive foam according to claim 1, having a
density of less than about 40% of the theoretical density, wherein the
foam has a peel adhesion of greater than about 20 N/cm and a compression
set of less than about 20% and wherein the foam comprises:
a) from about 20 to 35% by weight of at least one olefinic polymer having a
density less than 0.91 g/cm3 and a torsion modulus of less than 18 MPa;
b) from about 30 to about 60% by weight of at least one tackifying resin;
c) from about 5 to about 15% by weight of at least one plasticizing oil;
and
d) from about 2 to about 25% by weight of expandable particulate materials
comprising a polymeric shell and a volatilizable liquid core.
12. A pressure sensitive adhesive foam having a peel adhesion greater than
about 10 N/cm, comprising from about 99.5 to about 70% by weight of a
pressure sensitive adhesive polymer composition and from about 0.5 to
about 30% by weight of an particulate material comprising glass spheres,
wherein
the pressure sensitive adhesive polymer composition comprises at least one
olefinic polymer, having a density of less than 0.910 g/cm3 and a torsion
modulus of less than 18 MPa, and at least one tackifying resin.
13. A pressure sensitive adhesive foam according to claim 12, comprising:
a) from about 5 to about 80% by weight of at least one olefinic polymer
selected from the group consisting of polyethylene, polyproplyene,
polybutene and polymethyl-pentene, and copolymers thereof, and mixtures
thereof;
b) at least one tackifying resin in an amount sufficient to give the
adhesive foam a peel adhesion of at least 10 N/cm; and
c) from about 0.5 to about 30% by weight of glass spheres.
14. A pressure sensitive adhesive foam according to claim 12, comprising:
a) from about 10 to about 50% by weight of at least one olefinic polymer;
b) from about 15 to 80% by weight of at least one tackifying resin;
c) from about 0.5 to 15% by weight of at least one plasticizing oil; and
d) from about 2 to about 20% by weight of glass spheres.
15. A pressure sensitive adhesive foam according to claim 12, comprising:
a) from about 20 to about 35% by weight of at least one olefinic polymer;
b) from about 30 to 60% by weight of at least one tackifying resin;
c) from about 2 to 20% by weight of at least one plasticizing oil; and
d) from about 5 to about 15% by weight of glass spheres.
16. A method for joining at least one plastic surface to a substrate,
comprising the steps:
a) bringing the pressure sensitive adhesive foam of claim 1 into contact
with a plastic surface;
b) applying pressure to form a laminate of the pressure sensitive adhesive
foam and the plastic surface;
c) bringing a portion of the laminate consisting of the pressure sensitive
adhesive foam into contact with the substrate; and
d) applying pressure to form an assembly comprising the plastic surface,
the pressure sensitive adhesive and the substrate, whereby a force of at
least 5 N/cm must be applied to separate the pressure sensitive adhesive
foam from the plastic surface in the laminate.
17. The method of claim 16, wherein the plastic surface is a decorative
trim piece comprising polypropylene and the substrate is a vehicle body.
18. A method for joining at least one plastic surface to a substrate,
comprising the steps:
a) bringing the pressure sensitive adhesive foam of claim 12 into contact
with a plastic surface;
b) applying pressure to form a laminate of the pressure sensitive adhesive
foam and the plastic surface;
c) bringing a portion of the laminate consisting of the pressure sensitive
adhesive foam into contact with the substrate; and
d) applying pressure to form an assembly comprising the plastic surface,
the pressure sensitive adhesive and the substrate, whereby a force of at
least 5 N/cm must be applied to separate the pressure sensitive adhesive
foam from the plastic surface in the laminate.
19. The method of claim 18, wherein the plastic surface is a decorative
trim piece comprising polypropylene and the substrate is a vehicle body.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to pressure sensitive adhesive foams and in
particular to pressure sensitive adhesive foams which are easily
compressed and conform to irregular surfaces. The invention further
relates to a method of processing these pressure sensitive adhesive foams.
2. Technology Review
Pressure sensitive adhesives (PSA) that can be extruded are well known.
Examples of pressure sensitive adhesives include rubbers mixed with the
proper tackifying resins, cured acrylics, and interpenetrating polymer
networks containing blocked copolymers in a polyurethane network.
These pressure sensitive adhesives (PSA) all suffer from the common
limitation of being relatively hard to compress. The pressure sensitive
adhesives therefore do not conform easily to irregular surfaces, a
property that is vital to ensure 100% wetting and therefore good adhesion.
Generally, a limitation such as this could be overcome by making a
composition cellular or foamed. Foams are pliable, conform easily to
irregular surfaces and can be produced by either physical (e.g., frothing
with nitrogen before the polymeric mass sets) or chemical (incorporation
of a porophoric agent such as azodicarbonamide which undergoes a chemical
decomposition under heat to produce gaseous bubbles) means. Pressure
sensitive adhesive foams produced by either of the above techniques,
however, suffer from another limitation. Because of their inherent tack,
these pressure sensitive adhesive foams when compressed tend to
irreversibly deform due to adherence between opposite sides of the cells
in the cellular structure.
Presently, because of this limitation adhesive foams are produced by
coating non-adhesive foam substrates with thin layers of pressure
sensitive adhesives. These products both conform to irregular surfaces and
are pressure sensitive thereby overcoming the limitations of solid
pressure sensitive adhesive extrusions and pressure sensitive adhesive
foams. These products are, however, relatively complicated to produce and
cannot be used for extruded profiles. Furthermore, these products show
relatively poor adherence to non-polar plastic surfaces.
The foams of the invention are characterized by superior adherence to
non-polar plastic surfaces, compared to the acrylic adhesive coated foams
of the art. Unlike the foams of the art, the foams of the invention have
acceptable peel test values from difficult to adhere non-polar plastic
surfaces, including decorative trim pieces made of polypropylene and used
on products such as automotive bodies and other vehicle surfaces,
manufactured appliances, and home and office furnishings and equipment.
The foams of this invention are inherently adhesive foam products which
reversibly deform upon compression. This invention also describes a
process for producing the above inherently adhesive foamed product,
preferably utilizing expandable particulate materials, or, in some
instances, glass spheres, to prevent interior foam collapse and adhesion.
SUMMARY OF THE INVENTION
The present invention relates to a pressure sensitive adhesive foam with a
percentage of theoretical density less than 90 wherein the foam has a peel
adhesion of greater than about 1 N/cm and a compression set under constant
deflection of less than about 60 percent. The present invention further
includes a pressure sensitive adhesive foam comprising a thermoplastic
block copolymer; a tackifying resin; an isocyanate; a polymer comprising a
backbone of selected from the group consisting of polybutadiene, polyester
and polyether, wherein the polymer contains at least 2 active hydrogens
capable of reacting with the isocyanate; and expandable particulate
materials.
The present invention further includes a pressure sensitive adhesive foam
comprising a thermoplastic olefinic polymer or copolymer, having a density
less than 0.91 g/cm3 and a torsion modulus less than 18 MPa, and a
tackifying resin; expandable particulate materials, or glass microspheres;
and, optionally, plasticizing oil.
The invention finally further comprises a method of forming the above foam.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a pressure sensitive adhesive foam having
a density that is less than 90% of the theoretical density, wherein the
foam has a peel adhesion of greater than about 1 N/cm and a compression
set under constant deflection of less than about 60 percent.
The foam has a percentage of theoretical density less than 90, preferably
less than about 70 percent, more preferably less than about 50 percent,
and most preferably less than about 40 percent. The material from which
the foam is made has a density that is the "theoretical density". The foam
formed from this material has a reduced density and the extent of the
reduction is indicated by the percentage of the theoretical density
represented by the density of the blown foam material.
The foam has a peel adhesion of greater than about 1 N/cm, preferably
greater than about 5, more preferably greater than about 10, and most
preferably greater than about 20 N/cm. As used herein, "peel adhesion" is
the adhesive strength of the foam expressed as the force needed to remove
the foam from a prescribed surface as measured by ASTM D903 method.
The meaning of compression set for purposes of this specification is
compression set under constant deflection which is the recovery of a foam
after a constant deflection. ASTM Standard D 1667-76, paragraphs 21 to 25,
which are incorporated herein by reference describes the test method for
determining compression set with the following modification. As noted in
the Examples 1 and 2, below, certain specimens were compressed to 50% of
their original thicknesses, rather than to 25% of their original
thicknesses as specified in the test method.
The foam has a compression set of less than about 60 percent, preferably
less than about 40 percent, more preferably less than about 20 percent,
and most preferably less than about 10 percent.
The foam is produced by first mixing a pressure sensitive adhesive
composition with expandable particulate materials. The mixture may be
coated onto a substrate (e.g., a release film), or extruded (e.g., with
screw extruder or high pressure pump) into a sheet or film through a flat
die or into other geometries, such as a round or semi-circle bead, through
a rounded die or otherwise formed to a desired shape by molding or other
means known in the art for shaping plastic materials. The viscosity of the
mixture may be adjusted depending on whether the mixture is coated,
extruded or formed into a shape. The mixture can either be heated just
prior to, during or after coating, extrusion or forming to a temperature
at which substantially all of the expandable particulate material expands.
The foam can subsequently be cured if necessary.
When utilizing polyolefinic polymers as the elastomers in the adhesive
formulation, the foam may be produced as described above, or it may be
foamed by traditional chemical blowing techniques, with or without the
addition of glass microspheres or the expandable particulate material, or
by physical foaming techniques, with or without the addition of glass
microspheres or the expandable particulate material, or by a combination
of techniques and materials.
The pressure sensitive adhesives which may be used include adhesives which
are compounded to be pressure sensitive by blending an elastomer with
tackifying resins, plasticizers and other ingredients, and adhesives which
consist of polymers that are inherently pressure sensitive and require
little or no compounding. Examples of elastomers which are blended with
tackifying resins include natural rubber; and block copolymer adhesives
such as for example polystyrene-polybutadiene-polystyrene (SBS),
polystyrene-polyisoprene-polystyrene (SIS),
polystyrene-poly(ethylene/butylene)-polystyrene (S-EB-S), and
polystyrene-poly(ethylene/propylene)-polystyrene (S-EP-S). Examples of
inherently adhesive polymers which can be used with or without tackifiers
to create foams include acrylics; butyl rubber; polyisobutylene; and
silicones.
Certain low density, olefinic elastomers, including polymers and copolymers
having a density of less than 0.91 g/cm3 and a torsion modulus of less
than 18 MPa (i.e., "soft olefins", having a torsion modulus measured as
described in Example 3, below), are suitable for use herein in combination
with tackifying resins. Olefins having a density of less than 0.875 g/cm3
and a torsion modulus of less than 3.7 Mpa are preferred. Suitable olefins
include those described in U.S. Pat. No. 5,475,075 to Brant et al., which
is hereby incorporated by reference. The Brant olefins are polymerized
using a cyclopentadienyl metallocene catalyst system ("metallocene
polymers") and include a range of densities from 0.85-0.95 g/cm3. Only
those metallocene polymers having a density of less than 0.91 g/cm3 which
also are soft polymers may be used herein.
As used herein, "metallocenes" refers to polymerization catalyst systems
such as the system disclosed in U.S. Pat. No. 5,191,052, hereby
incorporated by reference. Metallocenes are complex combinations of a
metal atom compound with cyclopentadienyl groups (Cp). The metallocenes
are a "sandwich complex" arrangement of two Cp groups and a Group IV
Transition Metal (Ti, Zr, Hf, Cr). Such catalysts are also named "single
site" or "constrained geometry" catalysts. The metallocenes differ
significantly in structure and reactivity from the conventional
Ziegler-Natta catalysts used in the conventional polymerization of
ethylene polymers and copolymers. The metallocenes typically yield low
bulk density in contrast to conventional catalysts for ethylenic polymers.
The metallocene catalysts are single site catalysts and they control the
orientation of each monomeric unit added to the polymeric chain. The
olefinic polymers produced with these catalysts have a uniform
-compositional distribution and all polymer molecules within such
materials have substantially similar compositions. Some copolymers
prepared with metallocene catalysts contain long-chain branches within the
ethylene backbone of the molecules. In contrast, conventional linear low
density polyethylene typically does not contain long chain branches.
Conventional ethylenic polymers have a wide compositional distribution and
differ significantly in physical and mechanical properties, such as
crystallinity, from metallocene polymers having substantially equivalent
molar compositions and average molecular weights. For example, the
metallocene polymers useful in the pressure sensitive adhesives of the
invention are amorphous thermoplastic materials, having a much lower
crystallinity than conventional linear low density polyethylene.
Suitable olefins in addition to metallocene polymers, include, but are not
limited to homopolymers and copolymers of ethylene, propylene, butene and
methylpentene, having the density and softness characteristics specified
above, whether or not polymerized using a metallocene catalyst system.
Copolymers of ethylene are preferred, especially alpha-olefinic
copolymers.
In forming an elastomer based pressure sensitive foam, the elastomer or
rubbery polymer provides the elastic component while a low molecular
weight tackifying resin constitutes the viscous component. Therefore, for
these elastomer systems, it is the tackifying resin which ultimately
determines the viscoelastic behavior and the final properties of the
finished adhesive. Further, tackifier resins can also be used in
inherently adhesive polymers to increase the adhesion. Examples of
tackifying resins which can be used include rosins and rosin derivatives;
and hydrocarbon tackifier resins which further include aromatic,
aliphatic, mixed aliphatic/aromatic, heat-reactive, terpene resins and
modified or special resins.
Additives can be added to vary the properties and aging of the pressure
sensitive adhesive foam. Examples of additives which can be used include
antiblocking agents, antioxidants, antistatic agents, biocides, colorants,
couplings agents, curing agents, flame retardants, heat stabilizers, low
profile additives, lubricants, mold-release agents, odorants,
plasticizers, slip agents, ultraviolet stabilizers, urethane catalysts,
viscosity control agents and combinations thereof.
The expandable particulate material useful in the present invention can be
swellable or non-swellable in aqueous or organic liquid, and preferably is
insoluble in water or organic liquids. The expandable particulate
comprises a polymeric shell having a central core comprised of a fluid,
preferably liquid, material. A further requirement is that the overall
dimensions of the expandable particulate increase upon heating at a
specific temperature.
Expandable particulates include those materials comprised of a polymeric
shell and a core of at least one other material, either liquid or gaseous,
most preferably a liquid at room temperature. A liquid core is
advantageous because the degree of expansion is directly related to the
volume of change of the core material at the expansion temperature. For a
gaseous core material, the volume of expansion expected can be
approximated from the general gas laws. However, expandable particulates
comprising liquid core material offer the opportunity to provide much
larger volume changes, especially in those cases where a phase change
takes place, i.e., the liquid volatilizes at or near the expansion
temperature. Gaseous core materials include air and nonreactive gases, and
liquid core materials include organic or inorganic liquids. The expansion
function can also be supplemented by the addition of other conventional
blowing agents.
The preferred expandable particulate materials have shells surrounding a
fluid material. Examples of shell materials include copolymers of vinyl
chloride and vinylidene chloride, copolymers of vinyl chloride and
acrylonitrile, copolymers of vinylidene chloride and acrylonitrile, and
copolymers of styrene and acrylonitrile. Further can be mentioned
copolymers of methyl methacrylate containing up to about 20 percent by
weight of styrene, copolymers of methyl methacrylate and up to about 50
percent by weight of ethyl methacrylate, and copolymers of methyl
methacrylate and up to about 70 percent by weight of orthochlorostyrene.
The unexpanded microspheres contain fluid, preferably volatile liquid,
i.e., a blowing agent, which is conventional for these expandable
particles. Preferably, the blowing agent is 5 to 30 percent by weight of
the expanded particle. The microspheres can be added in different manners,
as dried particles, wet cakes, or in a suspension. The microspheres can
also be added in a pre-expanded form.
The unexpanded particulates preferably are in the size range of from about
1 to about 100 um, more preferably from about 2 to about 30 um, and most
preferably from 2 to about 10 um. After expansion, the volume of
expandable particulate increases by a factor of at least 2, preferably by
a factor of at least 3, and most preferably by a factor of at least 4, and
may even be is high as a factor of about 10.
An example of an expandable particulate material is Expancel.RTM. polymeric
microspheres (Nobel Industries, Sundsvall, Sweden) which expand from an
approximate diameter of 10 um in the unexpanded form to an approximate
diameter of 40 um after expansion. The corresponding volume increase is:
V.sub.f /V.sub.i =(r.sub.f /r.sub.i).sup.3 =4.sup.3
or 64 fold, where V.sub.f and r.sub.f are the final volume and radius of
the expandable particulate, respectively, after expansion, and V.sub.i and
r.sub.i are the corresponding initial values for the unexpanded
particulate.
The expandable particulate is normally obtained by suspension
polymerization. A general description of some of the techniques that can
be employed and a detailed description of various compositions that are
useful as expandable particulates can be found in U.S. Pat. No. 3,615,972.
A further description of compositions useful as expandable particulate can
be found in U.S. Pat. No. 4,483,889. Both patents are herein incorporated
by reference.
Examples of commercially available expandable particulate materials useful
in the present invention include those made of poly(vinylidene
chloride-co-acrylonitrile) such as Expancel.RTM. 820, Expancel.RTM. 642,
Expancel.RTM. 551, Expancel.RTM. 461, and Expancel.RTM. 051 expandable
particulate. Other commercially available materials having similar
constructions are available. For example, one comprising a shell of
methacrylonitrile-acrylonitrile copolymer, available as Micropearl.RTM.
F-80K microbubbles (Matsumoto Yushi-Seiyaku Co., Ltd., Japan) are also
useful as expandable particulate materials in the present invention.
A wide variety of blowing or raising agents may be incorporated within the
foaming process of the present invention. These agents can be volatile
fluid forming agents such as aliphatic hydrocarbons including ethane,
ethylene, propane, propene, butene, isobutene, butane and isomers,
cyclobutane, pentane and isomers, cyclopentane, hexane and isomers,
cyclohexane, neopentane, acetylene, heptane, or mixtures thereof or other
such aliphatic hydrocarbons having a molecular weight of at least 26 and a
boiling point below the range of the softening point of the shell.
Other suitable blowing agents are halocarbons such as perfluorobutanes,
perfluoropentanes, perfluorohexanes, fluorotrichloromethane,
dichlorodifluoromethane, chlorotrifluoromethane, trichlorotrifluoroethane,
heptafluorochlorocyclobutane, hexafluorodichlorocyclobutane, and
hydrohalocarbons such as CHF.sub.3, CHClF.sub.2, CH.sub.3 CHF.sub.2, and
tetralkyl silanes such as tetramethyl silane, trimethylethyl silane,
trimethylisopropyl silane, and trimethyl-n-propyl silane all of which are
commercially available.
The shape of the expandable particulate material is preferably spherical
but is not restricted to being spherical, i.e., it may be irregular. Other
shapes can easily be envisioned such as urnlike as described in U.S. Pat.
No. 3,615,972. The shape and orientation of the expandable particulate in
the pressure sensitive adhesive help to determine the anisotropy of the
expansion step. Where essentially spherical expandable particles are used,
heating leads to isotropic expansion of the article, i.e., there is no
preferred direction of expansion and all three axes expand uniformly so
that the overall shape of the article does not change, only its size.
Other physical constraints that may have been imposed on the article prior
to expansion may lead to less than perfect isotropic expansion where
essentially spherical expandable particles are used.
As a result of the expansion of the expandable particulate material, the
volume of the pressure sensitive material increases. The percent volume
increase is dependent on a number of factors including factors such as the
amount of expandable particulate material in the article and the molecular
weight of the polymeric shell of the particles. The decrease in density of
the article is inversely proportional to the volume and porosity increase
in the article.
A preferred embodiment of the present invention is a pressure sensitive
adhesive foam comprising an olefinic polymer or copolymer having a density
of less than 0.91 g/cm3 and a torsion modulus of less than 18 Mpa, a
tackifying resin, and expandable particulate materials. A tackifying
system including the tackifying resin and a plasticizing oil is preferably
used.
The olefinic polymer or copolymer preferably comprises from about 5 to
about 80 percent by weight of the total composition of the pressure
sensitive adhesive components, (i.e., all components except the expandable
particulate materials), more preferably from about 10 to about 50 percent
by weight, and most preferably from about 20 to about 35 percent by
weight.
Another preferred embodiment of the present invention is a pressure
sensitive adhesive foam comprising a thermoplastic block copolymer; a
tackifying resin; an isocyanate; a polymer comprising a backbone selected
from the group consisting of polybutadiene, polyester and polyether,
wherein the polymer contains at least 2 active hydrogens capable of
reacting with the isocyanate; and expandable particulate materials.
The thermoplastic block copolymer or elastomers are non-reactive with all
other components in the composition. Examples of suitable copolymers
include: styrene-isoprene-styrene block copolymers,
styrene-butadiene-styrene block copolymers, ethylene-propylene rubbers,
polyethylene-acrylate, styrene-butadiene, styrene-isoprene,
styrene-ethylene-butylene-styrene, 10 ethylene-propylene-diene terpolymer
rubbers, and ethylene vinyl acetate.) The thermoplastic block copolymer
preferably comprises from about 5 to about 80 percent by weight of the
total composition of the pressure sensitive adhesive foam comprising
components, (that is all components except the expandable particulate
materials), more preferably from about 10 to about 50 percent by weight,
and most preferably from about 10 to about 35 percent by weight.
The tackifying resin preferably comprises from about 15 to about 80 percent
by weight of the total composition of the pressure sensitive adhesive
foam, more preferably from about 25 to about 70 percent by weight, and
most preferably from about 30 to about 60 percent by weight. Examples of
types of tackifier resins which can be used include rosin and rosin
derivatives, aromatic hydrocarbon resins, aliphatic hydrocarbon resins,
mixed aliphatic/aromatic resins and terpene resins. The tackifier is
preferably a hydrocarbon resin. Examples of hydrocarbon tackifier resins
include glycerine rosin ester, hydrogenated pentaerythritol ester,
hydrogenated glycerine ester, modified tall oil rosin, polymerized rosin
and rosin ester.
Various plasticizing oils, which are themselves tackifying materials, may
be used in combination with the tackifying resins to increase tack at
lower temperatures. The plasticizing oils are preferably used with the
tackifying resins in formulations containing the olefinic polymers as the
elastomer component of the adhesive. The combination of plasticizing oils
and tackifying resins may be used at the same weight percentages as the
tackifying resins alone. Adhesive formulations preferably contain about
0.35 to about 30 percent, by weight of the pressure sensitive adhesive
components (all components except the expandable particulate materials
and/or glass spheres), of plasticizing oil, more preferably about 2 to 20
percent, and most preferably, 5 to 15 percent. Suitable plasticizing oils
include, but are not limited to, dewaxed and solvent refined parafinic
oils, low molecular weight polybutenes, and other, similar hydrocarbons
existing in a predominately liquid state at room temperature, and
combinations thereof.
The active-hydrogen containing polymer comprises a backbone selected from
the group consisting of diene polymers and copolymers, polyesters, olefin
polymers and copolymers, acrylate copolymers, polyethers and mixtures
thereof, and contains at least 2 active hydrogens capable of reacting with
the isocyanate terminated monomer. The polymer preferably comprises from
about 5 to about 70 percent by weight of the total composition of the
pressure sensitive adhesive foam, more preferably from about 5 to about 50
percent by weight, and most preferably from about 10 to about 25 percent
by weight. Examples of these polymers include polyester diols such as
Dynacoll.RTM. manufactured by Huls; Lupranols.RTM. manufactured by BASF;
polybutadienediols such as PolyBD.RTM. manufactured by Atochem;
polyetheramines such as Jeffamine.RTM. manufactured by Texaco; hydroxyl
grafted ethylene vinyl acetates such as Evathane.RTM. manufactured by
Atochem; poly-e-caprolactones such as Capa.RTM. manufactured by Solvay;
and mixtures thereof.
The isocyanate component can be any one of those typically used in such
formulations including tetramethylene diisocyanate, (TMDI); isophorone
diisocyanate, (IPDI); methylene diisocyanate, (MDI); toluene diisocyanate,
(TDI); polyphenyl polymethyl polyisocyanate, (PPPI); p-diphenyl methane
diisocyanate; and the like. The preferred isocyanate is TMDI. The
isocyanate is added in amounts to give a ratio of isocyanate groups to
active hydrogen-containing groups of from about 0.25 to about 1.75 more
preferably from about 0.5 to about 1.5 and most preferably from about 0.75
to 1.25. It is also possible to use components that yield isocyanates
under reaction conditions. This includes the so-called "blocked"
isocyanates in which the isocyanate group is reacted with a blocking
compound such as a phenol or a phenol derivative that protects the
isocyanate group from reaction with air or water under ambient conditions
but which is stripped off under reaction conditions.
The expandable particulate materials preferably comprise from about 0.5 to
about 35 percent by weight of the total composition of the pressure
sensitive adhesive foam, more preferably from about 2 to about 25 percent
by weight, and most preferably from about 5 to about 20 percent by weight.
The glass microspheres used with the polyole finic polymers preferably
comprise from about 0.5 to about 25 percent by weight of the total
composition of the pressure sensitive adhesive foam, more preferably from
about 2 to about 15 percent by weight, and most preferably from about 5 to
about 10 percent by weight. Suitable glass microspheres for use in the
invention may be obtained from PQ Hollow Spheres, Ltd., Yorkshire,
England, under the Armospheres 150 tradename.
The olefinic polymers may be cross-linked before, during or after following
formation of the adhesive foam. Cross-linking may be carried out by
chemical means, including but not limited to treatment with peroxides
(e.g., Perkadox BC or Perkalink 301 cross-linkers available from Flexsys
N.V., Woluwe, Belgium), ionic agents or silanes, or by physical means,
including but not limited to electron beam and gamma-ray radiation (Cobalt
60 source). When carried out with the tackifying resins and plasticizing
oils described in Examples 3 and 4, below, chemical cross-linking with
peroxides improved the temperature resistance, but decreased the peel
strength of the adhesive foam. The opposite effect was observed with the
same adhesive foams when subjected to physical cross-linking with either
electron beam or gamma-ray radiation. One skilled in the art will
recognize that the effects of cross-linking adhesive foam compositions
will vary depending upon the components in the adhesive and the linking
agent selected. Any of a variety of means may be selected by the
practitioner for use herein depending upon the properties required of the
foam during use.
As an alternative to crosslinking, or in conjunction with crosslinking, an
interpentrating polymeric network may be created in the pressure sensitive
adhesive formulation containing the olefinic polymers. Suitable networks
include, but are not limited to, the isocyanate-reactive diene polymer
systems described above for use with acrylic pressure sensitive systems.
The network increases the thermal stability of the resultant pressure
sensitive adhesive foam.
In order that persons in the art may better understand the practice of the
present invention, the following Examples are provided by way of
illustration, and not by way of limitation. Additional background
information known in the art may be found in the references and patents
cited herein, which are hereby incorporated by reference.
EXAMPLES
Example 1
This example is a comparison between non-adhesive foams which are coated
with a pressure sensitive adhesive and a intrinsically pressure sensitive
adhesive foam.
Preparation of Masterbatch of the Pressure-Sensitive Foam
The masterbatch is made in a Z-blade mixer provided with two counter
rotating Z shaped blades that are able to thoroughly mix even viscous
elastomers with one another. The mixing space is steam jacketed, and the
temperature of the materials mixed can be controlled between 80 and
160.degree. C., by regulating the steam pressure in the mixer jacket.
The temperature in the mixer is held at about 150.degree. C. and the
different components are introduced in the following order and weight
proportions:
SBS Rubber (Vector 4111), 100 parts
Tackifying Resin (Regalite R101), 200 parts
CaCo.sub.3 (Setacarb OG), 9 parts
Parafinic Oil (Enerpar 10), 30 parts
Polyetherdiol (Lupranol 2001), 75 parts
Catalyst (Texacat T30), 5 parts
Plastic Spheres (Expancel DU091), 33 parts
Before introducing the Expancel microspheres, the temperature is lowered to
100.degree. C. After completion of the mixing, the composition is unloaded
while hot enough to flow easily, on to thick siliconized paper.
Production of the Foam
Mixing the masterbatch with 8 parts by weight of Vestanat TMDI (the
isocyanate) is accomplished using a Brabender type machine, with two
counter-rotating arms. The mixing is realized in the narrow space between
the arms and the walls of the mixer. A typical amount to mixed was 50 g.
Working temperature was 100.degree. C., and speed of the arms 50 RPM.
Mixing time is about 1 minute. The mixed product is collected on a
siliconized Mylar (PET) film. Another sheet of that film is laid on top of
the product, and a film is shaped under a press at 100.degree. C.
Thickness of the film is 0.3 mm. This film is then cured and foamed in an
oven at 150.degree. C. keeping the Mylar on both sides.
The foam according to the invention thus produced was compared with a
commercial PUR foam laminated on both sides with a pressure sensitive
adhesive and sold by Norton Plastics Products Corp. under the registered
trademark "Normount V-2830". This is identified in the Tables below as
"C-2". The product according to the invention is also compared with a
product, identified as "C-1", which is a 140 kg/m.sup.3 polyethylene foam
coated with an acrylic PSA.
PSA Foam Properties/Measured by C-1 C-2 Invent.
Density (Kg/m.sup.3) ASTM D1667-76 305 600 400
Peel Adhesion (N/cm) ASTM D903 9 12 >22
Shear Adhesion (N/cm.sup.2) ASTM D1002 80 80 110
Tensile Adhesion (N/cm.sup.2) ASTM D897 75 65 120
Elongation at break (%) ISO 1926 210 220 185
Tensile Strength (N/cm.sup.2) ISO 1926 230 110 95
For the shear tests the method was modified by changing the speed from 1.3
mm/min to 10 mm/min. The samples were conditioned at room temperature for
24 hours before testing. Adhesion tests were made on stainless steel
except that tensile adhesion was between aluminum T-blocks. Also in the
tensile adhesion test the sample was 25.4 mm.times.25.4 mm square and the
speed of testing was 300 mm/min. No dwell time was provided. Measurement
of all the above parameters was carried out on a tensile Instron Type 1122
machine.
Adhesion..Diff. Substrates (N/cm) C-1 C-2 Invent.
Stainless Steel 9 12 >22
Glass -- 14 >22
Polypropylene -- 3 12
Adhesion after aging (N/cm) C-2 Invent.
after 10 min. @ RT 11 36
after 24 hr. @ RT 21 >48
after 24 hr @ RT + 5 hr @ -30.degree. C. 15 >10 *
+ 7 days @ 70.degree. C. 25 >44
+ 3 days in warm 22 32
moisture
after waxing compd. aging 15 24
after dewaxing compd. aging 18 >50
after washing solution aging 16 20
after alcohol aging 15 >27
* indicates that the foam tore apart
Example 2
This example is a comparison of the compression set of a 5 foam that is
chemically blown (by an excess of isocyanate and its reaction with
moisture) and a foam that is made using expandable particulate
(Expancel.RTM.).
Samples 3, 4 and 5 are made using the same process as is described in
Example 1. Samples 1 and 2 were also made according to the process of
Example 1 except for the omission of the polyetherdiol. The diisocyanate
is mixed with the masterbatch in the Brabender. The film made under the
press is put at 70.degree. C., 100% humidity for 24 hours, for foaming and
reticulation.
Sample 3 is the product according to the invention described in Example 1.
Ingredient
Nature Name 1 2 3 4 5
SBS Rubber Vector 4111 100 100 100 100 100
Tackifying Resin Regalite R101 200 200 200 200 200
CaCO.sub.3 Setacarb OG 9 9 9 9 9
Paraffinic Oil Enerpar 10 30 30 30 30 30
Polyetherdiol Lupranol 2001 -- -- 75 75 75
Catalyst Dabco T12 0.6 0.6 -- -- --
Catalyst Texacat T30 -- -- 5 5 5
Diisocyanate LupranatMP130 80 40 -- -- --
Diisocyanate Vestanat TMDI -- -- 8 8 8
Plastic spheres ExpancelDU091 -- -- 33 -- --
Glass spheres Armospheres -- -- -- 8 --
150 um
The compression set was determined using ASTM Standard Test Method D
1667-76, paragraphs 21 to 25. The following modification, however, was
made to the test method. Instead of the test specimen being deflected 25%
of its original thickness, the specimen is deflected to 50% of its
original thickness.
The specific gravity was measured using ASTM D1667-76 The force to compress
was measured using ASTM D1667-76, except that the samples were compressed
to 30% of their thickness rather than 25% at a speed of 10 mm/min.
Property Units 1 2 3 4 5
Specific gravity Kg/m.sup.3 500 800 400 860 950
% of theoretical % 53 84 42 90 100
density
Compression set % 61 35 11 41
Force to compress N/cm.sup.2 8.4 16.2 10.3
Example 3
A group of olefinic polymers were used to prepare foamed pressure sensitive
adhesives from the following composition.
Olefinic Polymer Adhesive Formulation
Adhesive Composition Parts
Olefinic polymer (a) 100
Tackifier resin (b) 200
Plasticizer oil (c) 50
Expandable particles (d) 20
(a) See Table below.
(b) ECR 404 resin, obtained from Exxon Chemical Europe, Machelen, Belgium.
(c) Enerpar 10 oil, obtained from BP Chemicals, Zwijndrecht, Belgium.
(d) Expancel 091DE80 particles, obtained from Expancel, Sundwall, Sweden.
The adhesive compositions were foamed by a method similar to the method
described in Example 1, above, except that all mixing was carried out in a
Brabender plasticorder mixer and the mixer was preheated to a temperature
of 120.+-.10.degree. C., the rotation of the roller arms was set at 50
rpm, and the polymers and quantities described above were used in place of
the SBS Rubber formulation of Example 1. After about two minutes of
mixing, a homogeneous melt was obtained and the temperature was decreased
to 90.degree. C. and the remaining components of the adhesive formulation
were mixed with the molten polymer. The expandable particles were added
after the temperature of the mixture was less than 90.degree. C. After
mixing, the mixture was removed from the mixer and was laminated in a
preheated press at 100.degree. C. between two sheets of siliconized PET to
the thickness needed to yield the final adhesive product after foaming.
Foaming was conducted by placing the preformed sheet into an oven
preheated to a temperature sufficient to expand the Expancel particles,
i.e., 150.degree. C. for 15 minutes.
Peel adhesion from stainless steel and from polypropylene and compression
set were measured by the methods described in Examples 1 and 2, above.
Results are shown below, along with hand tack observations and the density
and torsion modulus of the olefinic polymers.
polymer torsion peel peel compres-
olefinic density modulus hand adhesion adhesion sion set
polymer g/cm3 MPa tack steel polyprop %
C-3 0.900 18 none <1 <1 *
C-4 0.912 12 none <1 <1 *
6 0.917 34 none <1 <1 *
7 0.896 4.4 low <1 <1 *
8 0.875 3.7 low <1 <1 *
9 0.870 1.9 high >16 6 7.7
10 0.868 1.15 high 15 6 2.4
* The foam made from these samples was not usable and samples were not
tested for compression set.
Samples 6 (Exceed.TM. 350A60, a metallocene: ethylene/hexene copolymer,
m.p.=119.degree. C.), 7 (Exact.TM. 4015, a metallocene: ethylene/butene
copolymer. m.p.=83.degree. C.), 10 (Exact 5008, a metallocene:
ethylene/butene copolymer), and C-4 (Escorene.TM. 655 low density
polyethylene) olefinic resins were obtained from Exxon Chemical Company.
Samples 9 (Engage.TM. EP 8500, a metallocene: ethylene/octene copolymer,
m.p.=56.degree. C.) and 8 (Engage.TM. KC 8852, a metallocene:
ethylene/octene copolymer) olefinic resins were obtained from Dow Chemical
Company, and sample C-3 (DFDB 9042 NT-linear low density ethylene
copolymer) resin was obtained from Union Carbide Corporation.
Torsion Modulus Measurements
Polymer torsion modulus was measured by die cutting a 10 mm in diameter
sample from a sheet of polymer which had been hot pressed at 120 C to
yield a 1 mm thick sheet. The sample was tested in a Stresstech rheometer
(a universal controlled stress rheometer) by placing a sample between two
parallel plates (5 mm in radius)(r), applying a normal force of 10 N to
the upper plate and measuring the gap (h) between the plates. The gap was
recorded to an accuracy of 1/1000 mm. A sinusoidal stress was then applied
to the upper plate at a frequency equal to 1 Hz and an amplitude equal to
10.000 Pa, and the sinusoidal deformation was recorded. The strain
(.gamma.) is calculated from the angle amplitude .theta. using the
equation: .gamma.=(.theta..times.r)/h. The torsion complex modulus G* is
calculated by dividing the stress (i.e., 10.000 Pa) by the strain.
Suitable adhesive properties and foam compression set characteristics were
obtained using olefinic polymer samples having a density less than 0.910
g/cm3 and a torsion modulus of less than 18 MPa.
Example 4
Additional pressure sensitive adhesive foam compositions were prepared
using different tackifying resins and plasticizing oils with the Engage
8500 (sample 9) and Exact 5800 (sample 10) resins to yield a series of
samples having calculated theoretical densities of 960.+-.20 Kg/m3, and
foam densities of 341-465 Kg/m3 (by ASTM D1667-76 method). The foam
densities represent 35 to 50% of the theoretical densities of the adhesive
formulations.
Peel strengths from stainless steel and from polypropylene were conducted
on all samples by the methods described in Examples 1 and 2, and the
results are given below. Compression set tests were conducted by the
method described in paragraphs 21-25 of ASTM D1667-76 with a 25%
deflection.
Parts by Weight
Sample No. 9a 9b 9c 10a 10b 10c 10d
Component
Olefinic Polymer
Sample 9 100 100 100
Sample 10 100 100 100 100
ECR 404 Tackifier 200 200 200
Escorez 1304 Tackifier 200 200
Piccotac 95 Tackifier 200 200
Enerpar 10 Oil 50 50 50 50 50 50
Hyvis 10 Oil 50
Expancel Particles 20 20 20 20 20 20 20
Test Results
Foam Density Kg/m3 383 407 367 390 426 380 407
Peel St. Steel N/cm >16 0 >37 15 >31 >24 >20
Peel Polypropylene 8 >33 >33 6 >28 >24 >20
N/cm
Compression set % 7.7 21 8 2.4 26 13 16.2
Results demonstrate the superior adhesion to plastic surfaces, such as
polypropylene, of the foams of the invention in comparison the the acrylic
adhesive coated foams of the prior art (see Example 2 peel tests results
for C-2 sample). Formulations containing certain combinations of the
olefinic polymer samples 9 and 10 with some tackifying resins, and/or
plasticizing oil showed superior adhesion results and would be used where
pressure sensitive foams having higher peel adhesion strength are needed.
Best results were obtained with sample 9c (Engage 8500) ethylene/octene
copolymer in combination with Piccatoc 95 tackifier and Hyvis 10 oil.
Additional samples having foam densities of 223-843 Kg/m3 were prepared
from sample 10 resin using the adhesive formulations shown below. Glass
microspheres were used in place of the Expancel particles in some of these
samples.
Formulations Containing Glass Spheres
Sample No.: 10c 10f 10g 10h 10i
Component
Olefin (a) 100 100 100 100 100
Tackifying resin 200 200 200 200 200
(b)
Plasticizing Oil 50 50 50 50 50
(c)
Expancel Particles 5 20 50 0 0
Glass Spheres (d) 0 0 0 20 50
Test Results
Foam Density 674 390 223 843 824
Peel Stainless >17 15 7 >28 17
Steel
Compression N/cm2 18 14 13 26 28
(a) Exact 5800 resin (sample 10).
(b) ECR 404 resin.
(c) Enerpar 10 oil.
(d) Armospheres 150 particles (hollow glass micro balloons, average
particle size 75 microns, and specific gravity 0.60-0.75 g/cc) obtained
from PQ Hollow Spheres Ltd., Yorkshire, England.
In samples containing the glass spheres, the concentration of spheres
affected the peel strength of the foam, yielding higher peel values at
lower concentrations. The expandable particles yielded a soft foam, having
a range of densities depending upon the concentration of particles
contained in the foam sample. All samples yielded acceptable pressure
sensitive adhesive foams.
It is understood that various other modifications will be apparent to and
can be readily made by those skilled in the art without departing from the
scope and spirit of the present invention. Accordingly, it is not intended
that the scope of the claims appended hereto be limited to the description
set forth above but rather that the claims be construed as encompassing
all of the features of patentable novelty which reside in the present
invention, including all features which would be treated as equivalents
thereof by those skilled in the art to which the invention pertains.
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